Gas turbine engines (“GTE's”) produce power by extracting energy from a flow of hot gas produced by combustion of fuel in a stream of compressed air. In general, GTE's have an upstream air compressor coupled to a downstream turbine with a combustion chamber (“combustor”) in between. Energy is released when a mixture of compressed air and fuel is ignited in the combustor. The resulting hot gases are directed over the turbine's blades, spinning the turbine, thereby, producing mechanical power. In typical GTE's, one or more fuel injectors direct some type of fossil fuel into the combustor for combustion. Combustion of fossil fuel results in the production of some undesirable constituents in GTE exhaust emissions. These undesirable constituents include nitrogen oxide (NO) and nitrogen dioxide (NO2), which are collectively referred to as NOx. In some countries, government regulations restrict the allowable level of NOx that may emitted by GTE's.
The amount of NOx emissions from a GTE increases with the flame temperature in the combustor. Therefore, one technique used by GTE manufacturers to meet NOx regulations is to reduce the flame temperature in the combustor of the GTE. Low flame temperature in the combustor may be achieved by reducing the fuel content in the fuel-air mixture fed into the combustor and by thoroughly mixing the fuel in the air before the fuel-air mixture is directed into the combustion chamber. Such a well mixed fuel-air mixture with a lower fuel content is referred to as a lean premixed mixture. While this lean premixed mixture reduces NOx emissions, reducing the fuel content in the mixture below a threshold value may cause the resulting flame to be unstable. The unstable flame may cause undesirable pressure oscillations within the combustor, eventually leading to smothering of the flame (called “lean blow-out”).
To provide a stable flame while meeting NOx emission regulations, some GTE fuel injectors provide for multiple fuel paths or streams, such as a main fuel stream and a pilot fuel stream. In such a system, the main fuel stream provides lean premixed fuel to the combustor for low NOx operation, while the pilot fuel stream provides a source of rich fuel to the combustor for flame stabilization and startup. U.S. Pat. No. 5,404,711 ('711 patent), a patent issued to the assignee of the current disclosure, on Apr. 11, 1995, describes a GTE fuel injector with main and pilot fuel streams. While the injector of the '711 patent has proven to be reliable and robust, and has achieved wide commercial success, the assembly providing the pilot fuel stream of the '711 patent are permanently attached to the rest of the injector structure to provide a good seal against fuel and air leakage. Since GTE fuel injectors are positioned close to the combustion flame, the components of the injector may be subject to high temperature damage mechanisms. While the permanent attachment of the pilot assembly of the '711 patent prevents fuel and air leakage, replacement of a damaged pilot component in a field environment becomes difficult. The present disclosure is directed to solving one or more of the problems set forth above.